Effects of uniaxial strain on stability and structural evolution of vacancy clusters in copper

The effects of [0 0 1] uniaxial strain on the energetics, stable structures, and structural evolution of vacancy clusters with different structure and orientation characteristics in copper have been studied by molecular statics simulation. The dependence of binding energies as functions of strain for different cluster types, including linear, planar, and body types, shows complicated behavior. The binding energies of both linear and planar clusters monotonously vary with the strain from −10% to 10%, while those of body clusters decrease with increasing both tensile and compressive strain. According to the variation of the binding energies, it has been suggested that the linear and planar clusters tend to align parallel (perpendicular) to the strain axis under tensile (compressive) strain. Moreover, both the {0 0 1} planar cluster and body cluster become the dominant types when the clusters grow under high strain. Then, a mechanism that the local structure around a vacancy cluster tends to approach the ideal lattice structure without defects and strain has been applied to explain the effects of the uniaxial strain on the relative stability of the vacancy clusters. This tendency is closely tied to the level of the atomic relaxation which can be measured by the average atomic displacement of the nearest-neighbor atoms surrounding the vacancy cluster.